Internal combustion engines may use variable cam timing (VCT) to improve fuel economy and emissions performance of a vehicle. One method of variable cam timing uses an Oil Pressure Actuated device (OPA), such as a vane type cam phaser. The phaser may be controlled by an electromechanically actuated spool valve that directs oil flow to one side or the other of the vane. The performance of this device is thus dependent on oil pressure, which may be set lower for fuel economy or to reduce parasitic loads under nominal conditions.
The inventors herein have recognized that under certain conditions, VCT phasers may not reach a desired position, e.g., when camshaft phaser temperatures are higher than the oil sump temperature or when the VCT phasers are worn. Further, this condition may be exasperated when the oil pressure is set lower for fuel economy or to reduce parasitic loads. Reduced oil pressure may also reduce the phasing velocity of VCT phasers which may negatively affect engine response, turbo spool up time, and the ability to meet optimal Brake Specific Fuel Consumption due to engine breathing, for example.
In some examples, VCT phasers are equipped with a locking pin in their home position to prevent rattle noise. These pins may be pushed out the by the same oil that moves the cams. However, there is a race condition when the cams are first commanded to move so that if the cam moves first it may jam the pin in the locked position preventing further movement of the cam.
In one example approach, to at least partially address these issues, an engine method is provided. The method comprises, in response to an operating condition, adjusting a valve coupled to a hydraulic variable camshaft timing actuator to initiate camshaft phasing and adjusting an oil pressure supplied to the valve based on a camshaft phaser position. In some examples, if a camshaft phaser locking pin is in a home position, the method may further comprise reducing the oil pressure supplied to the valve for a predetermined time interval to a threshold amount to unlock the locking pin but not move the camshaft phaser and then increasing the oil pressure supplied to the valve to move the camshaft phaser.
In this way, oil pressure may be boosted when the phasing position in not achieved so that a pump (e.g., a Variable Oil Pump (VOP)) output is increased to help push the cams to a desired position. Further, the amount of oil pressure compensation may be proactive and reactive. For example, the error may be saved in a weighted additive manner for future use and may be used to estimate an age of the VCT phasers. Additionally, the VCT pin unlocking can be made more controllable by reducing the oil pressure to a pressure that the pin preferentially reacts and the cam phaser does not. Further, since the oil pressure may be set lower while still achieving VCT control and increased during select conditions when needed by the VCT system, fuel economy may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.